A hydraulic aggregate of the above type is described in WO 2006/103199 A1 (Wagner). This hydraulic aggregate comprises a reservoir provided with a submerged motor submerged into the oil contained in the reservoir. The submerged motor has no casing so that the oil is able to reach all functional components of the motor and will also fill out the gap between stator and rotor. The motor is arranged to drive a multi-piston pump comprising distributed individual pumps. The individual pumps are cyclically actuated by an eccentric which is mounted on the motor shaft. A pump of this type has a star-shaped configuration, and, within the cylindrical reservoir, the pump is arranged in a cross-sectional plane. The hydraulic aggregate is provided with a motor control unit arranged on the housing of the reservoir and accommodated within a separate device housing.
Customary hydraulic aggregates for power wrenches are used in an environment where no specific risk of explosions prevails. This allows for the use of an electric motor for driving the multi-piston pump. For hydraulic aggregates which have to be run in an environment with explosion hazard, this known hydraulic aggregate with its uncased motor will not be suited. The electric motor may happen to inflame the oil contained within the reservoir. Providing an explosion-proof encapsulation would require a considerable increase in volume and weight.